1. Field of the Invention
The present invention relates to a wear-detecting probe for a braking element and to a braking element provided therewith.
2. Description of the Related Art
A known wear-detecting probe is identified by the numeral 1 in FIG. 4. The probe 1 has a stepped holder 2 with a leading end and a narrow section 2A adjacent the leading end. A wire 3 is folded in U-shape and held in the holder 2 with the fold of the wire 3 exposed from the leading end of the holder 2. The probe 1 is used with a brake shoe 4 that has a base plate 5 with a mount hole 6 and a friction member 7 mounted on the base plate 5. The narrow section 2A of the holder 2 is introduced through the mount hole 6 and projects into the friction member 7. A clip 8 is used to press a stepped surface 9 of the holder 2 resiliently against the edge of the mount hole 6. The friction member 7 is abraded by a mating rotary element during normal use, and a specified amount of abrasion will cut the folded section of the wire 3.
The mating rotary element that contacts the folded section of the wire 3 exerts a bending force on the narrow section 2A of the holder 2, as shown by an arrow in FIG. 4. This bending force may concentrate a stress on a corner 9A at the base end of the narrow section 2A to crack or break the holder 2 at the corner 9A. The concentration of the stress can be alleviated if the corner 9A is rounded. However, the stepped surface 9 of the holder 2 determines the projected amount of the holder 2 by being properly brought into contact with the edge of the mount hole 6. Thus, if the corner 9A of the narrow section 2A is rounded, the stepped surface 9 cannot be brought precisely into contact with the edge of the mount hole 6. Accordingly, the corner 9A should remain a right-angle, and the above problem cannot be dealt with easily.
The present invention was developed in view of the above problem and an object thereof is to avoid the concentration of a stress while maintaining a mounting precision of a holder.
The invention is directed to a wear-detecting probe to be assembled or mounted with a braking element that can contact a rotary element. The probe is adapted to detect whether a degree of abrasion of the braking element has reached a wear limit based on whether a detection wire has been cut or abraded. The wear-detecting probe comprises a stepped holder with a leading end and a narrow section at the leading end. A wire is arranged in the holder and is exposed from the leading end of the holder. The holder is insertable into a mount hole in the braking element so that a stepped surface of the holder substantially contacts an edge of the mount hole. The stepped surface of the holder is recessed over substantially the entire periphery of a base end of the narrow section to form a groove, and a radially inner corner of the bottom of the groove is rounded.
A bending force acts on the small-diameter portion of the holder when the detection wire contacts the mating rotary element and may concentrate a stress on the inner corner of the bottom of the groove. However, the corner or of the groove is rounded, and hence the stress concentration can be avoided. Thus, cracks and the like can be prevented.
The groove is formed around the base end of the narrow section. Thus, the stepped surface can be held properly in contact with the edge of the mount hole while maintaining a flat contact surface. Therefore, the holder can be assembled precisely with the braking piece.
The detection wire preferably is folded substantially in a U-shape and is held in the holder such that a folded section is exposed from the leading end of the holder.
Preferably, the rounded portion is substantially semi-circular.
The narrow section preferably is provided at its leading end with a supporting projection to support the folded section of the detection wire in an axial and/or radial direction.
A flange preferably is provided for mounting the wear-detecting probe to the braking element via a biasing means that biases the stepped surface of the wear-detecting probe toward the mount hole.
The wire preferably is exposed toward the leading end by being drawn-out and inserted into corresponding openings in the narrow section.
The invention also is directed to a braking element with a wear-detecting probe as described above. The wear detecting probe is assembled with a braking piece that can contact a rotary element and can detect whether a degree of abrasion of the braking element has reached a working limit based on whether a detection wire has been cut.
The mount hole preferably is in a base plate of the braking element.
A biasing means may be provided for biasing the stepped surface of the wear-detecting probe toward the mount hole. The biasing means may be mountable on the wear-detecting probe via a mount member.